Data storage devices including, e.g., those normally provided as part of, or in connection with, a computer or other electronic device, can be of various types. In one general category, data is stored on a rotating (or otherwise movable) data storage medium. A read head, a write head and/or a read/write head is positioned adjacent desired locations of the medium for writing data thereto or reading data therefrom. The head may include separate or integrated read and write elements. One common example of a data storage device of this type is a disk drive (often called a hard disk drive, “HDD,” or “fixed” disk drive).
Typically, the information is stored on each disk in nominally concentric tracks, which are divided into sectors. The read/write head (or transducer) is mounted on an actuator arm capable of moving the head to access various radial positions of the disk. Accordingly, the movement of the actuator arm allows the head to access different tracks. The disk is rotated by a spindle motor at a high speed, allowing the head to access different sectors on the disk.
Although many concepts and aspects pertaining to the present invention will be described herein in the context of a disk drive, those skilled in the art, after understanding the present disclosure, will appreciate that advantages provided by the present invention are not necessarily limited to disk drives.
In an idealized drive configured with nominally concentric data tracks, if a read/write head is kept a constant radial distance from the (nominal) axis of rotation, there will be no change in the radial distance (if any) from the read/write head to the desired data track, as the disk rotates. In actuality, however, many factors can contribute to deviations from this ideal condition such that small tracking correction forces must be applied to the read/write head to maintain the head sufficiently aligned with a desired data track, as the disk rotates, although some amount of tracking error can be tolerated. Most modern disk drives provide a servo tracking system for seeking a target track and/or making tracking corrections to assist in maintaining tracking within acceptable ranges.
Typically, as part of a manufacturing or setup procedure (prior to normal use for data read/write), a hard disk drive is provided with a plurality of servo “bursts,” markers or sectors. The purpose of these bursts is to provide location information to components of the head-positioning and/or tracking system. Generally, a plurality of servo bursts are positioned around a given track. Typically, over various portions (“zones”) of the radial extent of the disk, the bursts are circumferentially aligned, from one track to the next, defining a plurality of servo “wedges.”
Proper operation of a disk drive typically involves maintaining the read write head at a preferred location with respect to the adjacent disk surface. Many hard disks are configured to provide their best performance when the read write head is maintained at a distance (or “fly height”) from the disk surface of a few nanometers. If the read/write head is located more than a tolerance amount from the preferred nominal fly height, there could be loss of data and/or effective loss of data storage capacity of the disk drive. Further, if the read write head is sufficiently close to the disk surface, a condition known as “head-disk interference” (HDI) occurs. Head-disk interference can (but need not always) involve contact of the head with the disk surface and has the potential to cause temporary or permanent physical damage to the HDD.
In many HDD manufacturing processes, attempts are made to detect whether HDDs that are being manufactured have occurrences of HDI or other anomalies. The detection of an anomaly may, depending on severity or other conditions, result in “failing” the drive. A drive which is “failed” (tagged as defective) may be subjected to various treatments, including removal from the product stream, repair and/or analysis. While it is useful to identify, during manufacturing, those HDDs which have occurrences of HDI, the amount of time involved in such detection can adversely affect the throughput and/or effective cost per unit of HDD manufacturing. Furthermore, previous HDI detection typically occurred after (or in conjunction with) a substantial amount of other configuration or testing procedures. Meaning that, by the time a drive was “failed” for HDI occurrences, an undesirably large amount of effort and funds had already been expended on the drive, again adversely affecting HDD manufacturing throughput and effective per-unit cost. Accordingly, it would be useful to provide a method, system and apparatus for detecting HDI which is of relatively short duration and/or occurs relatively earlier in the manufacturing process, as compared to previous approaches.
In some previous approaches, HDDs which had occurrences of HDI might be “failed” in a manner that may not specifically indicate that HDI was the cause of the failure (such as tests which detect an anomaly that can arise from any of a number of causes). Such failure data has limited utility in identifying possible problems in equipment or procedures of manufacturing. Further, some previous approaches provided little, if any, information pertinent to the location on the disk where HDI occurs, and/or the number of HDI occurrences and/or the severity of HDI. Thus, these approaches provided little information usable in deciding the disposition of the failed drive (repair, disassemble and use selected parts, scrap, etc.). Accordingly it would be useful to provide a method, system and apparatus which can distinguish HDI occurrences from other sources of failure or potential failure, and/or can provide information regarding the location of, number of, and/or severity of HDI occurrences.